1. Field of the Invention
This invention relates to a probe for extracting hot sample gas, which probe comprises an inner tube for conducting sample gas and a jacket, which surrounds the inner tube and defines a passage for conducting a liquid coolant.
2. Description of the Prior Art
If processes in which hot gases are formed are to be controlled in dependence on the composition of said hot gases, sample gas must be extracted from the reaction chamber through an extraction probe. Being exposed to the high temperatures of the hot gases, the outside surfaces of the extraction probes must be cooled. On the other hand, the cooling of the outside surface of the probes may result in a temperature drop below the dew point temperature of the sample gas being extracted so that condensate may undesirably form in the inner tube of the extraction probe. A condensation will be particularly undesirable if the sample gas is dust-laden, such as is the case, e.g., during the calcination of a ground mixture of the raw materials used in the production of cement. Dust entrained by the gas will mix with the condensate to form a sludge, which may form a crust on the inner tube of the extraction probe and may restrict the flow area therein. It is known that such a temperature drop below the dew point temperature can be avoided in that at least in the inner tube for conducting the sample gas the coolant is always maintained at a temperature above the dew point temperature of the sample gas. But such cooling will require a relatively expensive control and will give rise to special problems in all cases in which the dew point temperature of the sample gas exceeds the evaporation temperature of the liquid coolant consisting in most cases of water.